Stabilization of ethyl cellulose



Patented July 24, 1951 STABILIZATION OF ETHYL CELLULOSE Peter Van Wyck, -Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Original application June 10, 1944,

Serial No. 539,793. Divided and this application May 7, 1948, Serial No. 25,793

This invention relates to the stabilizationpf fl ethyl cellulose and their compositions which retain their-viscosity and good color after exposure to heat and oxygen.

It has been previously recognized that cellulose ethers must be so prepared as to withstand the degradation effects of heat and oxygen. Although various methods of stabilizing cellulose ethers to make them resistant to decomposition have been suggested, such as hydrogenation, treatment with diazomethane, etc., no simple means of stabilization has proved thoroughly satisfactory;

Prolonged storage of the flake, and the heat and oxygen present during molding operations cause embrittlement of' the compositions made therefrom, due to viscosity degradation of the ether and, in'addition thereto, objectionable color formation-p Previously proposed methods of stabilizing cellulose ethers, such as low pH adjustment of the flake, sometimes correct one or the other of these defects, but the simultaneous stag bilization of bothcolor and viscosity to a satis} factory degree is difficult, and usually impossible, to perform by previously known procedures. To obtain a satisfactory end product, such as film, lacquer or molded article, it is necessary to have flake stability as well as composition stability,

since, Without the former, the latter is usually im' possible.

Now, in accordance with this invention, the

viscosity stability of cellulose ethers and of their compositions has been greatly improved, while maintaining good color stability, by the addition of a material containing copper in free or combined state, either to the flake or to the ether fcomposition. It has been found that copper and copper compounds exert a" definite stabilizing effect on cellulose ethers or their compositions,

Claims. (Cl. 106-193) protecting them from degradation when exposed to heat or oxygem- 7 As illustrative of carrying out the invention, the following examples are typical:

EXAMPLE 1 A medium-viscosity ethyl cellulose was dissolved in 70-30 toluene-alcohol. To portions of this solution were added the amounts indicated in Table I of powdered copper and various copper compounds Filmswerecastfrom the solutions, and the films thus formed were heated for 16 hoursat 120 C. in air, after which they were tested, as hereinafter described, for viscosity. Viscosity measurements were also made on portions of the films before heat-treatment. Table I compares results obtained with original (unstabilized) and stabilized ethyl cellulose.

- TABLE I Per Cent P C t O Rfegention er on u o iscos- Slammer in Film ity After 16 Hours No stabilizer 42. 7 Powdered co'pper. 0. 0015 93. 4 Cupric nitrate" 0. 0012 96. 5 Cupric sulfate... 0. 0010 89. 8 Cupric chloride. 0.0015 89. 8 Cuprous chloride" 0. 0015 '81. 5 Cupric phosphate 0.0015 51. 3 Cupric carbonate 0.0010 55. 4 Copper arsenate 0. 0015 53. 5 Cupric oxide 0. 0014 87. 3 Copper'ammonium c 0.0015 90. 7 Copper acetate 0.0016 87. 6 Copper citrate I 0 0015 60. 7 Copper bcnzoyl benzoate ;l 0.0013 89. 0

To 100 grams of granular medium viscosity ethyl cellulose (44.7% ethoxyl) was added 600 grams of isopropyl alcohol. To thi suspension, 0.025 gram hydrated cupric acetate was added with stirring; .After mild agitation for '2 hours, theethyl cellulose was drained and then dried at C. in" vacuum. Substantially all of the copper compound was absorbed.

To grams of dry ethyl cellulose, identical with that used in Example 2, was added 600 grams of distilled water. To this suspension, an aqueous solution containin 0.0375 gram of hycompound was absorbed.

EXAMPLE 4 T.o..400.. grams or.nake...etnyi teiiiiiose. .identica with that used in Examples 2 and 3, was added 3 0.15 gram of hydrated cupric acetate which had previously been ground to pass a 100-mesh sieve. The copper compound was uniformly distributed by subsequent tumbling for minutes.

Table II presents a comparison between the 5 untreated ethyl cellulose and the stabilized ethyl cellulose produced by the method described in Examples 2, 3, and 4.

4 EXAMPLE 8 Medium-viscosity ethyl cellulose (46.5% ethoxyl) was treated with dilute acid according to the method described in U. S. Patent No. 1,448,091. To 400 grams of the resulting ash-free product was added 2,000 grams of isopropyl alcohol containing 0.048 gram cupric chloride.

The ethyl cellulose was stirred, drained, and

dried as described in Example 2 above.

TABLE 11 EXAMPLE 9 Ethyl cellulose, identical with that used in i Example 8, was treated according to the method sample 9 1 3 1 gg g gig g g e described in U. s. Patent No. 1,448,091. To 400 c y g 3 5 5 grams of the resulting ash-free product, suspended in 2,000 grams of 35% isopropyl alcohol, was added 0.02 gram cuprammonium hydroxide. fiff ethyl 358 16 Lightbwwn' Stirring, draining, and drying were carried out Eiilliyl cellluose from 328 152 Verytlight tarli),1 color a d rib d in Example 2 m ifil ft tse from 320 139 "i33 20 g lg fi z z xampe as ree e y ce ose an e e y ce uoses D 3 3 333 114 resulting from the treatments described in Examples 8 and 9.

TABLE IV Stability data on Examples 8 and 9 0.1.1.1 it??? A h iit a i. Pi

9. l' S SS 8 118 818 Sample Viscosity Hrs. at NazOOa P. P. M. P. R M. 160C. ofE.C. 0iE.C.

Per cent Ash-free ethyl cellulose 94 3. 0 nil 0 0 Ethyl cellulose from Example 8 94 80. 0 0. 010 120 17 Ethyl cellulose from Example 9 94 60.0 0. 020 50 37 EXAMPLE 5 To 200 grams of medium-viscosity ethyl cellulose (44.5% ethoxyl) were added 200 grams of water and 850 grams of 41% isopropyl alcohol to give a final mixture containing 33% isopropyl alcohol based on the total weight of the liquid present. The pH of the mixture was adjusted to 3.6 with glacial acetic acid, after which 0.024 gram hydrated cupric acetate was added. The sample was stirred, drained, and dried as described in Example 2.

EXAMPLE 6 Example 5 was repeated, the "only change being that a pH of 7.1 was used instead of the pH used in Example 5,

EXAMPLE '1 Example 5 was repeated, the only change being that a' pH of 8.2 was used instead of the pH used in Example 5.

Table III presents a comparison between the untreated ethyl cellulose and the ethyl celluloses prepared according to the methods described in Examples 5, 6, and 7.

As Table I shows, a wide variety of copper stabilizers is available. These include the inorganic salts, such as the sulfates, nitrates, arsenates, chlorides, carbonates, and phosphates; the organic derivatives, such as the citrates, acetates, and benzoates; complexes, such as cuprammonium hydroxide and chloride; and copper itself, in the form of copper or bronze dusts.

The stabilizers are effective in very small proportions, as shown by the tables and examples. From about 0.001% to 0.005% is a convenient range of copper concentrationwhich gives efiective stabilization; in general, a quantity between about 0,0005% and 0.03% is preferred. When relatively inactive substances, such as copper naphthenate or copper oxalate, are used, as much as about 1% may be necessary, but with the most active agents, such as copper nitrate (see Table V), as little as about 0.0002% gives satisfactory stabilization. In general, for all stabilizers, a quantity between 0.0002% and 1%, the percentage being that of copper on the basis of the cellulose ether stabilized, is utilized. Copper, in the form of copper nitrate, was incorporated in films in the quantities shown, after which the films were heat-tested in the manner hereinafter described.

TABLE V RPter gent f Per Cent e en 9 3 Viscosity Cu in F 11m After 16 Hours at C.

These data show that 0.00013% copper produces little stabilization. While 0.00026% copper gives very satisfactory stability, and, indeed, while quantities as low as about 0.0002% are effective, it is advisable to add a minimum of about 0.0005% to insure good stability throughout a large mass of plastic composition, wherein perfect uniformity of distribution might be difficult to obtain.

While ethyl cellulose is used in the examples to illustrate the invention, these stabilization treatments apply equally well to cellulose ethers generally, for example, other alkyl cellulose ethers such as methyl cellulose and propyl cellulose; aralkyl ethers such as benzyl cellulose; mixed ethers such as methyl-ethyl, methyl-benzyl, or ethylbenzyl celluloses; carboxy ether such as sodium 'carboxymethylcellulose. Water-soluble ethers and organic olvent-soluble types of ethers are included. All cellulose ethers are subject to the degradation processes herein described which occur when said ethers are subjected to heating and oxidation. The addition of copper or copper compounds to such ethers or their compositions con- 'stitutes an effective means for minimizing or changing the degradation mechanisms.

The degree of substitution and viscosity of the cellulose ethers do not affect the stabilizing action of the added copper or copper compounds. When ethyl cellulose is used, the commercially available types usually contain between about 44.5% and 50% ethoxyl. Formolded articles, a viscosity of about 100 centipoises is usually used, and films are frequently made up of 50-centipoise viscosity grade. Lower viscosity grades are usually used in lacquers, varnishes, etc., principally material of about 22 centipoises or less. All are effectively stabilized in accordance with this invention. v

Plasticizers for cellulose ethers, such as tributylphosphate, tricresylphosphate, triphenyl' phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diamyl phthalate, diphenyl phthalate; vegetable oil fatty acids, such as castor oil fatty acids; fatty alcohols, such as lauryl alcohol; vegetable oils and mineral oil, linseed oil, etc., may be incorporated in an amount necessary to the particular use to which the composition is to be put. In addition, there may be mixed with the cellulose ethers various compatible resins, such as wood rosin, hydrogenated rosin, gum Congo, dammar, cumar, phenolics, modified phenolics, alkyds, ester gum, shellac, etc., as well as fillers, pigments, and coloring matter. Swelling agents, such as methyl alcohol, ethyl alcohol, and mixed solvents, such as ethyl alcohol and acetone, may be used instead of the isopropyl alcohol shown in Example 2.

The amount of swelling agent used in the steeping bath is subject to wide variation, dependent upon the specific swelling agents, the steeping time, and the temperature employed. Concentrations between about 15% and 40% of the swelling agent have been found'suitable. However, use of a swelling agent is not essential.

The temperature of the steeping treatment may vary between about C. and about 100 C., but the range between about 15 C. and about 70 C. is preferred. The time of steeping may be from about minutes to several hours, but about 30 to 60 minutes is a preferred period."-' If noswelling agent isfused, as in Example 3,-the steeping time is usually betweenabout 1 to 3 hours.

As shown by Example 4, an effective way of adding powdered copper compounds is by incorporation with the dry grains, involving a simple tumbling operation to effect distribution. Although the use of copper acetate is shown by Example 4,bronze dust, copper dust, or finely-divided copper compounds other than the acetate may be added in the same manner. Another useful method of copper stabilization is the addition of copper or copper compounds during molding powder formation or in lacquer formation.

j The stability tests carried out on samples shown in Table I and V involved the heating of films at C. for 16 hours. The remaining samples were tested by the following method: Films 0.1 to 0.15 millimeter in thickness were prepared by spreading, on glass plates, 12.5% solution of the ethyl cellulose dissolved in 70-30 toluene-alcohol. The film was dried in air for 3 hour and in an oven at 70 C. for 2 hours. Sections of the film 6 by 3 inches were then cut and pleated by folding in accordion shape and placed in the bottom of a 10-inch test tube which was left open at the top. The test tube with the inserted film was placed in a forced draft oven adjusted to C. 3 1 C. and heated for 1 /2 hours. The film was then removed, immediately placed in a stoppered bottle, weighed after cooling, and made up to a 5% solution in 80-20 toluene-alcohol. The viscosity of the heat-degraded film solution was then measured at 25 C. and compared with the viscosity of another portion of the same film which had not been given the heat-treatment.

As shown by Table I, copper stabilization is effective regardless of the anionic component which has been added. However, as shown by Table III, the pH at which copper treatment is carried out usually predetermines the extent to which the copper compound i absorbed by the cellulose ether. While this table shows that the absorption of copper occurs over a wide pH range, the higher pHs cause greater copper absorption and, hence, are to be preferred.

The majority of treatments to which cellulose ethers are normally subjected for ash removal or viscosity degradation cause viscosity instability of the resultant product. However, as shown by Examples 8 and 9, this adverse acidic condition is counteracted by the addition of copper to the unstable material.

The advantages of the use of copper and copper compounds as stabilizer for cellulose ethers reside in the following: The copper and copper compounds are easily incorporated with the ethers at any stage of the aftertreatment or during lacquer or plastic formation; unlike numerous other stabilizers, viscosity is effectively protected against degradation by heat or oxygen without the concurrent formation of objectionable colored decomposition products; the extent of stabilization is excellent and superior to that obtained with most other stabilizers; and only extremely minute quantities of the stabilizers are ordinarily needed.

Thus, according to the present invention, copper-containing materials have been found to be very effective heat stabilizers for cellulose ethers and their compositions, with or without plasticizers and other ingredients. The terms copper-containing materials and materials containing copper are meant to include copper per 'se, bronzes and brasses, inorganic compounds and 7 tion, Serial No. 539,793, filed June 10, 1944, now Patent No. 2,445,374, issued July 20, 1948.

What I claim and desire to protect my Letters Patent is:

1. As a new composition of matter, an ethyl cellulose characterized by the presence therein of an agent capable of stabilizing the ether against the degrading efiects of heat and oxygen without reducing the viscosity of the ether, said agent being at least one material of the group consisting of copper, brass and bronze in powdered form and being present in an amount from about v 0.OCI02% to about 1%.

0.0002% to about 1%.

3. As a new composition of matter, an ethyl cellulose characterized by the presence therein of an agent capable of stabilizing the ether against the degrading effects of heat and oxygen without reducing the viscosity of the ether, said agent being copper dust in an amount from about 0.0002% to about 1%.

4. As a new composition of matter, an ethyl cellulose characterized by the presence therein of an agent capable of stabilizing the ether against the degrading effects of heatand oxygen without reducing the viscosity of the ether, said agent being bronze dust in an amount from about 0.0002% to about 1%.

5. As a new composition of matter, an ethyl cellulose characterized by the presence therein of an agent capable of stabilizing the ether against the degrading effects of heat and oxygen without reducing the viscosity of the ether, said agent being brass powder fin an amount from about 0.0002% to about 1%.

6. An ethyl cellulose plastic composition characterized by the presence therein of an agent capable of stabilizing the composition against the degrading eifects of heat without reducing the viscosity of the composition, said agent being copper powder in an amount from about 0.001% to about 1%.

7. As a new composition of matter, an ethyl cellulose characterized by the presence therein of an agent capable of stabilizing the ether against the degrading effects of heat and oxygen without reducing the viscosity of the ether, said agent being at least one material of the group consisting of copper, brass and bronze in powdered form and being present in an amount from about 0.0005% to about 0.03%.

8. As a new composition of matter, an ethyl cellulose characterized by the presence therein of an agent capable of stabilizing the ether against the degrading efiects of heat and oxygen without reducing the viscosity of the ether, said agent being elemental copper powder in an amount from about 0.0005% to about 0.03%.

9. In the process of preparing ethyl cellulose, the improvement comprising adding to a mass of granular cellulose ether at least one material of the group consisting of copper, brass and bronze in powdered form in an amount equivalent to between about 0.0002% and about 1% of copper based on the weight of the ether, and distributing the copper-containing material throughout the mass of the ether to stabilize the ether against the degrading effects of heat and oxygen.

10. In a process of preparing ethyl cellulose, the improvement comprising incorporating with the said ethyl cellulose at least one material of the group consisting of copper, brass and bronze in powdered form in an amount equivalent to from about 0.0002% to about 1% of copper based on the weight or the ether to stabilize the ethyl cellulose against degradation by heat and oxygen.

PETER VAN WYCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,086,543 Dreyfus July 13, 1937 2,086,591 Whitehead July 13, 1937 2,333,577 Koch Nov. 2, 1943 2,390,217 Krieger Dec. 4, 1945 2,445,374 Van Wyck July 20, 1948 

1. AS A NEW COMPOSITION OF MATTER, AN ETHYL CELLULOSE CHARACTERIZED BY THE PRESENCE THEREIN OF AN AGENT CAPABLE OF STABILIZING THE ETHER AGAINST THE DEGRADING EFFECTS OF HEAT AND OXYGEN WITHOUT REDUCING THE VISCOSITY OF THE ESTER, SAID AGENT BEING AT LEAST ONE MATERIAL OF THE GROUP CONSISTING OF COPPER, BRASS AND BRONZE IN POWDERED FORM AND BEING PRESENT IN AN AMOUNT FROM ABOUT 0.0002% TO ABOUT 1%. 